The present invention relates to liquid crystalline polymer films prepared from polymers of novel monomers having azobenzene mesogenic groups and supported in cross linked network structures. The present invention also relates to processes for the preparation of such polymer films. The present invention also relates to polymers of novel monomers having azobenzene mesogenic groups and processes for the preparation thereof, and to polymers prepared from such novel monomers. More particularly, the present invention relates to processes for the preparation of 4-[(4-cardanyl) azo] benzoic acid and its acryloyl derivative 4-[(4-acryloylcardanyl) azo] benzoic acid and their respective polymers poly 4-[(4-cardanyl) azo] benzoic acid and poly 4-[(4-acryloylcardanyl) azo] benzoic acid and includes a process for the cationic polymerisation of 4-[(4-cardanyl) azo] benzoic acid.
4-[(4-cardanyl azo] benzoic acid and 4-[(4-acryloylcardanyl azo] benzoic acid of formulae I and II are novel monomers having azobenzene mesogen. Poly 4-[(4-cardanyl) azo] benzoic acid and poly 4-[(4-acryloylcardanyl) azo] benzoic acid of formulae III and IV are their respective liquid crystalline polymers having azobenzene mesogen supported in a cross linked network structure. The cationic polymerisation of 4-[(4-cardanyl) azo] benzoic acid also gives rise to another liquid crystalline polymer of formula V. These compounds are prepared from inexpensive naturally occurring materials such as cashew nut shell liquid and its distillation product cardanol. 
Liquid crystalline (LC) polymers with cross linked networks are becoming attractive due to possibilities for freezing the LC phase (Shiota, A. and Ober, C. K. Prog. Polym. Sci., 1997, 22, 975; Morman, W. and Zimmermann, J. G., Macromolecules, 1996, 29, 1949; Morman, W., Trends in Polymer Science, 1995, 2(8), 2559; Koner, H. And Ober, C. K., Polym. Mater. Sci.Eng. Prepr., 1995, 73, 456; Morman, W. and Zimmermann, J. G., Macromol. Symp., 1995, 93,96; Wang, Y. H., Hong, H. L., Yang, F. S. and Hong, I. L., Polym. Mater. Sci.Eng. Prepr., 1994, 71, 678; Melissaris, A. P., Sutter, J. K., Litt, M. H, Scheiman, D. A. and Scheiman, M., Macromolecules, 1995, 28, 860; Hoyt, A. E. and Huang, S. J. J. Macromol. Sci.: Pure Appl. Chem., 1995, A32,1931; Hikmet, R. A. M., Lub, J. and Tol, A. J. W., Macromolecules, 1995, 28, 3313; Lai, W. W. and Chang, T. C., J. Polym. Sci., Polym. Chem. Ed., 1995, 33, 1075; Douglas, E. P., Langlois, D. A. and Benicewice, B. C., Chem. Mater., 1994, 6,1295; Mallon, J. J. and Adams, P. M. J. Polym. Sci., Polym. Chem. Ed., 1993, 31, 2249; Barclay, G. G. and Ober, C. K., Prog. Polym. Sci., 1993, 18, 899; Navarro, F., Macromolecules, 1991, 24, 6622; Peter, K. and Ratzsch, M., Macromol. Chem., 1990, 191, 1021; Taroze, R. V., Gubina, T. I., Shibaev, V. P., Plate, N. A., Pakin, V. I., Shamakova, N. A. and Shukov, F., Macromol. Chem. Rapid Commun., 1990, 11, 67; Mitchel, G. R., Davis, F. J. and Ashman, Polymer, 1987, 28, 639: Zentel, R. and Reckert, G., Macromol. Chem., 1986, 187, 1915; Finkelmann, H., Kock H. J. and Rehage, G., Macromol. Chem. Rapid Commun., 1981, 2, 317; Percec, V. (Ed), Liquid Crystalline Polymers, Parts 1-4, Prog. Polym. Sci., 1997, 22). These cross linked polymers pass through a mesophase during curing and retain a mesophase in the final state (Shiota, A. and Ober, C. K. Prog. Polym. Sci., 1997, 22, 975). By combining the ability to lock in an ordered network structure with the ability to macroscopically align the network, these materials can be used for preparation of films and bulk materials where highly ordered structures can be obtained. LC main chain/side chain polymers with cross linked networks can be prepared by chemical/thermal/photo-cross linking of reactive double bonds in the chain or by reaction with a cross linking agent or by copolymerisation (Morman, W. and Zimmermann, J. G., Macromolecules, 1996, 29, 1949; Koner, H. And Ober, C. K., Polym. Mater. Sci.Eng. Prepr., 1995, 73, 456; Wang, Y. H., Hong, H. L., Yang, F. S. and Hong, I. L., Polym. Mater. Sci. Eng. Prepr., 1994, 71, 678). Thus, investigations on a number of rigid rod liquid crystalline thermosets such as blacetylene rigid rod thermosets (Shiota, A. and Ober, C. K., Prog. Polym. Sci., 1997, 22, 975; Melissaris, A. P., Sutter, J. K., Litt, M. H., Scheiman, D. A. and Scheiman, M., Macromolecules, 1995, 28, 860; Douglas, E. P., Langlois, D. A. and Benicewice, B. C., Chem. Mater., 1994, 6, 1295), cyanate ester rigid rod thermosets (Barclay, G. G. and Ober, C. K., Prog. Polym. Sci., 1993, 18, 899), rigid rod epoxy thermosets (Carfagna, C., Amendola, E., Giaberini, M., Filiprov, A. G. and Bauer, R. S., Liq. Cryst, 1993, 13, 571; Dhein, R., Meier, H.-M., Muller, H.-P. And Gipp, R., German Offen 3622613, A1, 1988; Earls, J. D. and Hefner, R. E., Jr., Eur. Patent Appl. 379057, A2, 1990; Hefner, R. E., Jr. and Earls, J. D., Eur. Patent Appl. 475238, A2, 1992; Eirchmeyer, S., Muller, H.-P. and Karbach, A., Eur. Patent Appl. 445401, A2, 1991), bismaleimide rigid rod thermosets (Hoyt, A. E. and Huang, S. J. J. Macromol. Sci.: Pure Appl Chem., 1995, A32, 1931) and semirigid rod liquid crystalline thermosets (Shiota, A. and Ober, C. K. Prog. Polym. Sci., 1997, 22, 975; Hikmet, R. A. M., Lub, J. and Tol, A. J. W., Macromolecules, 1995, 28, 331) were reported. All these polymers employ the conventional networking using a multiple epoxy grouping or a diacetylene moiety or diacrylate moiety. No report on the formation of cross link through a side chain containing multiple double bonds could be found in patent literature or publications on cross linked liquid crystalline polymers. However, the side chain of cardanyl acrylate has been reported to be used in cross link formation in poly(cardanyl acrylate) which is not liquid crystalline (John, G. and Pillal, C. K. S., Macromol. Chem. Rapid Commun. 1992, 13, 255; John, G. and Pillal, C. K. S., J. Polym. Sci,Polym. Chem., 1993, 31, 1069; Pillal, C. K. S., in Handbook of Engineering Polymeric Materails, (Ed) N. P. Cheremisinoff, Marcel Dekker, New York (1997). Cardanol is a naturally occurring material and hence is inexpensive. The formation of the cross-linked polymer has been explained as due to the autocross linking of the unsaturated side chain of cardanyl unit (John, G. and Pillai, C. K. S., J. Polym. Sci,Polym. Chem., 1993, 31, 1069). This property of the cardanyl side chain can be used to form cross linked network structures for liquid crystalline polymers. Cardanol was shown to possess special structural features that allow it to be transformed into high performance polymers including liquid crystalline polymers (Pillal, C. K. S., Sherrington, D. C. and Sneddon, A., Polymer, 1992, 33, 3968; Saminathan, M., Pillai, C. K. S. and Pavithran, C., Macromolecules, 1993, 265 7103; Pillal, C. K. S., Sherrington, D. C. and Sneddon, Indian Patent Application No. 679/Del/92 dated Jul. 29, 1992; Saminathan, M. Pillal, C. K. S. and Pavithran, Indian Patent Application No. 2791/Del/92 dated Dec. 31 1992; Saminathan, M. , Pillal, C. K. S. and Pavithran, Indian Patent application No. 2972/Del/92 dated Dec. 31, 1992. In an earlier patent (Saminathan, M., Pillal, C. K. S. and Pavithran, C., Indian Patent Application No.2972/Del/92 dated Dec. 31, 1992), it was shown that a liquid crystalline polymer, poly[4-[hydroxy-2-pentadecyl)azo]benzoic acid] can be prepared from 3-n-pentadecyl phenol, the hydrogenated derivative of cardanol and that this polymer is potentially a non-linear optical (NLO) material (Saminathan, M., Pillai, C. K. S. and Pavithran, C., Macromolecules, 1993, 26, 7103). Azobenzene derivatives and polymers containing donor-acceptor groups in conjugation are known for their NLO activity (Sudesh Kumar, G., AZO Functional Polymers: Functional Group Approach in Macromolecular Design, Technomic Publication, Lancaster 1992; Sutherland, R. L., Handbook of Nonlinear Optics, Marcer Dekker, New York, 1996 and I-C. Khoo, F. Simoni, and C. Umeton, Novel Optical Materials and Applications, Wiley-VCH Publications, Weinheim, Germany, 1996). To retain the NLO property in a polymer, it is, however, important to prevent the dipole reversal or relaxation from their dipolar alignment. One of the methods recommended to arrest the relaxation is by introducing cross links during polling which xe2x80x9clock inxe2x80x9d dipole alignment due to the restricted molecular mobility.
Azobenzene derivatives and polymers containing donor-acceptor groups in conjugation are known for their non-linear optical activity. To retain the non-linear optical property in a polymer, it is, however, important to prevent the dipole reversal or relaxation from their dipolar alignment. One of the methods recommended to arrest the relaxation is by introducing cross links during polling which xe2x80x9clock inxe2x80x9d dipole alignment due to the restricted molecular mobility.
It is therefore important to obtain azobenzene derivatives capable of providing polymers which have non-linear optical activity.
The main object of the invention is to provide liquid crystalline polymer films and processes for the preparation thereof wherein the films are made of polymers with non-linear optical activity.
It is another object of the invention to provide novel monomers containing azobenzene mesogens and liquid crystalline polymers containing azobenzene mesogenic moieties supported in a cross linked network structures using a C15H27 hydrocarbon substituent with multiple double bonds suitable for making liquid crystalline polymer films.
It is another object of the invention to provide processes to prepare novel monomers containing azobenzene mesogens and liquid crystalline polymers and polymer films containing azobenzene mesogenic moieties supported in a cross linked network structures using a C15H27 hydrocarbon substituent with multiple double bonds.
It is another object of the invention to provide processes for the preparation of novel monomers containing azobenzene mesogens making use of a natural material, cardanol, which is cost effective.
It is a further object of the invention to overcome the problem of high cost of prior art monomers used to prepare liquid crystalline polymers.
It is another object of the invention to provide a process for the preparation of novel monomers containing azobenzene mesogen and polymers and polymer films thereof wherein the formation of cross links can also be controlled by controlling the rate of heating of the polymers.
The present invention relates to a process for the preparation of 4-[(4-cardanyl)azo]benzoic acid and 4-[(4acryloylcardanyl)azo]benzoic acid and their polymers poly4-[(4-cardanyl)azo]benzoic acid and poly 4-[(4-acryloylcardanyl)azo] benzoic acid. The present invention also provides a process for the cationic polymerisation of 4-[(4-cardanyl)azo]benzoic acid.
Accordingly, the present invention provides a process for the preparation of cross linked films of poly4-[(4-cardanyl)azo]benzoic acid and poly 4-[(4-acryloylcardanyl)azo] benzoic acid, comprising dissolving the polymer in a conventional organic solvent, evaporating the solvent, raising the temperature to 150-180xc2x0 C., annealing the polymers to obtain cross linked films exhibiting liquid crystalline phase behaviour.
In one embodiment of the invention, the solvent is selected from the group comprising of tetrahydrofuran, dimethyl acetamide, dimethyl form amide.
In another embodiment of the invention, the polymers are heated at a uniform heat rate of 5-10xc2x0 C. per minute to the desired temperature range.
In a further embodiment of the invention, the polymers are annealed at a temperature in the range of 150-180xc2x0 C. for 1 to 2 hours to obtain the fully cross linked polymer networks exhibiting liquid crystalline phase behaviour.
The invention also relates to novel monomers extracted from cardanol having azobenzene mesogens selected from 4-[(4-cardanyl)azo]benzoic acid and its acryloyl derivative 4-[(4acryloylcardanyl)azo]benzoic acid.
The invention also relates to a process for the preparation of 4-[(4-cardanyl)azo]benzoic acid and its acryloyl derivative 4-[(4acryloylcardanyl)azo] benzoic acid, said process comprising diazotising p-amino benzoic acid by any known method, adding a solution of cardanol in an organic solvent drop wise to the diazonium salt solution and crystallising it from an organic solvent to obtain 4-[(4-cardanyl)azo]benzoic acid, and if desired converting the said 4-[(4-cardanyl)azo]benzoic acid obtained to its acryloyl derivative and 4-[(4acryloylcardanyl)azo]benzoic acid by any known method.
In one embodiment of the invention, the diazotisation is effected using sodium nitrate in dilute hydrochloric acid at a temperature in the range of 0-5xc2x0 C.
In another embodiment of the invention, the ratio of p-amino benzoic acid and cardanol used is 1:1.
In a further embodiment of the invention, 4-[(4-cardanyl)azo]benzoic acid is converted to its acryloyl derivative 4-[(4acryloylcardanyl)azo]benzoic acid by reacting the monomer with acryloyl chloride.
The invention also relates to a process for the polymerisation of the novel monomers above, said process comprising subjecting the said novel monomers to one of polycondensation, free radical polymerisation or cationic polymerisation.
The invention also relates to a process for the preparation of poly4-[(4-cardanyl)azo]benzoic acid comprising subjecting 4-[(4-cardanyl)azo]benzoic acid to polymerisation by any known polycondensation technique using thionyl chloride and pyridine.
In one embodiment of the invention, the process for the preparation of poly4-[(4-acryloylcardanyl)azo] benzoic acid comprises subjecting 4-[(4-acryloylcardanyl)azo]benzoic acid to polymerisation by any known free radical polymerisation technique.
Another embodiment of the invention provides a process for the preparation of the cationic polymer of formula V of 4-[(4-cardanyl)azo]benzoic acid by subjecting the monomer to polymerisation by cationic mechanism in the presence of borontrifluoroetherate in dichloroethane at 100xc2x0 C. to obtain the said cationic polymer polymerised through the side chain unsaturation.
The invention also relates to novel polymers poly4-[(4-cardanyl)azo]benzoic acid and poly4-[(4-acryloylcardanyl)azo]benzoic acid of 4-[(4-cardanyl)azo]benzoic acid and its acryloyl derivative respectively, having azobenzene mesogens in network structures and the cationic polymer of formula V of 4-[(4-cardanyl)azo]benzoic acid, said cationic polymer being polymerised through the side chain unsaturation.
The invention also relates to a process for forming polymer films ahving azobenzene mesogens in crosslinked network structures comprising (a) diazotizing p-amino benzoic acid by known methods, adding a solution of cardanol in an organic solvent drop wise to the diazonium salt solution and crystallising 4-[(4-cardanylazo]benzoic acid so obtained from an organic solvent, (b) polymerising the novel monomer 4-[(4-cardanylazo]benzoic acid by known polycondensation technique using thionyl chloride and pyridine to give poly4-[(4-cardanylazo]benzoic acid or (c) reacting 4-[(4-cardanylazo]benzoic acid with acryloyl chloride to get the acryloyl derivative 4-[(4acryloylcardanyl)azo]benzoic acid, polymerising said acryloyl derivative by known free radical polymerisation technique to give poly4-[(4-acryloylcardanyl)azo] benzoic acid, or (d) polymerising the said 4-[(4-cardanyl)azo]benzoic acid by cationic mechanism using borontrifluoroetherate in dichloroethane at 100xc2x0 C. to get the cationic polymer of 4-[(4-cardanyl)azo]benzoic acid polymerised through the side chain unsaturation, (e) cross linking the polymers obtained above by controlled heating at a rate of 5-10xc2x0 C. per minute to a temperature of 150-180xc2x0 C. and annealing at this temperature for 1-2 hours and (f) dissolving the polymer prior to cross linking in solvents selected from tetrahydrofuran, dimethyl acetamide, dimethyl formamide and evaporating the solvent off by exposing the glass plate in a vacuum oven and raising the temperature to 150-180xc2x0 C. and annealing at this temperature for 1-1xc2xd hours to obtain cross linked films thereof exhibiting liquid crystalline phase behaviour.
In one embodiment the invention relates to a process for the preparation of 4-[(4-cardanyl)azo]benzoic acid and 4-[(4acryloylcardanyl)azo]benzoic acid and their polymers poly 4-[(4-cardanyl)azo] benzoic acid and poly4-[(4-acryloylcardanyl)azo] benzoic acid including a process for the cationic polymerisation of 4-[(4-cardanyl)azo]benzoic acid comprising (a) diazotising p-amino benzoic acid by known methods, adding a solution of cardanol in an organic solvent drop wise to the diazonium salt solution and crystallising it from an organic solvent, polymerising the novel monomer 4-[(4-cardanyl)azo]benzoic acid thus obtained by known polycondensation technique using thionyl chloride and pyridine to give poly4-[(4-cardanyl)azo]benzoic acid, (b) reacting 4-[(4-cardanyl)azo]benzoic acid with acryloyl chloride to get the acrylic derivative 4-[(4acryloylcardanyl)azo]benzoic acid, (c) polymerising said acryloyl derivative by known free radical polymerisation technique to give poly4-[(4-acryloylcardanyl)azo]benzoic acid or (d) polymerising 4-[(4-cardanyl)azo] benzoic acid by cationic mechanism using borontrifluoroetherate in dichloroethane at 100xc2x0 C. to get the cationic polymer of 4-[(4-cardanyl)azo]benzoic acid polymerised through the side chain unsaturation (e) and if desired converting the polymers obtained above to cross linked polymer films with azobenzene mesogens in network structures by cross linking the polymers under controlled heating at a rate of 5-10xc2x0 C. per minute to a temperature of 150-180xc2x0 C. and annealing at this temperature for 1-2 hours and (f) dissolving the polymer in solvents selected from tetrahydrofuran, dimethyl acetamide, dimethyl formamide and evaporating the solvent off by exposing the glass plate in a vacuum oven and raising the temperature to 150-180xc2x0 C. and annealing at this temperature for 1-1xc2xd hours whereby cross linked films exhibiting liquid crystalline phase behaviour.
In one embodiment of this invention, the monomer prepared is converted to its acryloyl derivative by any known method.
In one embodiment of this invention, the novel monomers prepared are 4-[(4-cardanyl)azo]benzoic acid and 4-[(4acryloylcardanyl)azo]benzoic acid.
The invention also provides a process for the preparation of polymers of the novel monomers containing azobenzene mesogens
In one embodiment of this invention, the polymerisation is done by (1) polymerising the monomer 4-[(4-cardanyl)azo]benzoic acid by known polycondensation technique using thionyl chloride and pyridine to give poly4-[(4-cardanyl)azo]benzoic acid, (2) reacting 4-[(4cardanyl)azo]benzoic acid with acryloyl chloride to get the novel monomer 4-[(4acryloylcardanyl)azo]benzoic acid, polymerising it by known free radical polymerisation technique to give poly4-[(4-acryloylcardanyl)azo]benzoic acid, or by (3) polymerising 4-[(4-cardanyl)azo]benzoic acid by cationic mechanism using borontrifluoroetherate in dichloroethane at 100xc2x0 C. to get the cationic polymer of 4-[(4-cardanyl)azo]benzoic acid polymerised through the side chain unsaturation.